In a typical wireless communications network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area and provide radio coverage over service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or beam being served or controlled by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB” or “gNodeB”. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
A Universal Mobile Telecommunications network (UMTS) is a third generation (3G) telecommunications network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface.
The continuously evolving wireless communications networks are expected to cover many different use cases and will be operating in many different frequency spectra. With a wide array of applications, frequency bands, i.e. sub-1 GHz to 100 GHz, bandwidths and different modes of operations, e.g. licensed vs. unlicensed, different radio requirements have to be fulfilled. These radio requirements are subject to the regulatory requirements in the specific geographical region, to the specific frequency band/sub-band, etc. . . .
Moreover, the regulatory constraints, radio frequency planning and device capability demand appropriate selection, and adaptation of circuitry of wireless devices, which is in its turn highly important in order to optimize performance of the wireless device as well as its power consumption.
The evolving fifth generation (5G) wireless communications networks are envisioned to overcome the limitations of existing cellular networks by allowing for higher data rates, improved user experience, lower energy consumption and satisfying the ever-increasing traffic demand. For this purpose, the need for additional spectrum beyond what was previously allocated to existing standards is emerging. The use of high frequency bands, including licensed, unlicensed and licensed-shared spectrum is a potential candidate to overcome the problem of scarce spectrum resources by allowing for wider bandwidths, more advanced antenna arrays and massive beam-forming.
In order for the evolving wireless communications networks to handle the envisioned growth in traffic volume, wider frequency bands, new spectrum, advanced antenna solutions and in some cases denser deployments are needed. In addition, a massive growth in the number of connected wireless devices as well as an increasingly wide range of new applications are expected in order to enable a well-functioning networked society, where information can be accessed and data shared anywhere and anytime, by anyone and anything.
Similarly, other evolving technologies, including the fourth generation (4G) wireless communications networks and Wi-Fi are challenged by the same demands.
Multi-antenna technologies have a key role in the design of modern Radio Access Technologies (RAT) due to their well-recognized benefits. Specifically, the multi-antenna technologies enable array gain, spatial multiplexing, and spatial diversity, which lead to improved coverage, capacity, and robustness. The multi-antenna features have significantly contributed to the success of LTE and continue driving its evolution. Multi-antenna technologies have an even larger relevance in high frequency bands. For instance, high frequency propagation is subject to several loss factors, starting from the high atmospheric attenuation, rain fade, foliage attenuation, building and wall penetration, diffraction and body/obstruction loss. While some of the mentioned loss aspects may be considered as minor problems for lower frequency bands, their impact becomes severe in millimeter wave ranges. This increased path-loss limits potential communications range, however high frequency bands allow for smaller frequency reuse distances, larger bandwidth and small beam width allowing for higher gain values, which in turn can compensate to some extent for the experienced higher path-loss.
As of today, licensed spectrum is primarily used for wide area networks. The license costs are significant but on the other hand, the licensed spectrum permits high transmission power, accurate cell planning and full frequency re-use without the need to apply schemes like Listen-Before-Talk (LBT). This ensures good coverage even in areas of sparse deployments. The exclusive use of the spectrum minimizes the risk of delay spikes and maximizes the capacity.
On the other hand, Wi-Fi, LTE License Assisted Access (LAA) and other emerging technologies, use unlicensed spectrum. Such technologies permit access to wide frequency bands given that a wireless device must ensure fair access to the spectrum. In some bands this is typically achieved by coexistence mechanisms such as LBT, wherein an energy detection just before a planned transmission burst may reveal that the spectrum is already used by another wireless device. Various back-off schemes are supposed to keep access delay short while making the spectrum sharing fair. Moreover, well-established constraints on the radio requirements of the various wireless devices are set by the regulations. The main purpose for having such restrictions is the aim of establishing fair coexistence between the different technologies that are operating in these unlicensed bands. These restrictions are region- and frequency band-specific and highly depend on the specific band allocation to the various applications. Hence, these factors and restrictions pose several design challenges on the evolving RATs.